Inventions of universal-jointed cycle trailer hitches for one-wheeled trailers were disclosed by Hazelett in U.S. Pat. No. 4,413,835 and by Hazelett, Bender, and Savage in U.S. Pat. No. 4,883,283. The hitches there described have proven highly serviceable. Together with a suitable one-wheeled trailer as described in the aforesaid patents, these universal-jointed hitches have proven readily capable of safely hauling cargoes of up to 40 kilograms or about 90 lbs, when attached to a typical bicycle. Moreover, universal-joint hitches do not permit the trailer to fall over unless the normally-upright bicycle also falls over.
However, the earlier of our prior-art hitches requires to be clamped high on the rear fork of the towing bicycle, an area now often occupied by brakes or by pannier-rack attaching lugs. Moreover, these prior-art hitches have been expensive to manufacture.
In the design of these prior-art hitches, no use was made of the pivoting capability of the seat post 72 of the bicycle. The current commercial range of seat posts includes many diameters from 30 to 24 millimeters. To make use of the seat post for attachment appears at first to require a great variety of sizes of hitch assembly that would be pivoted around it. Such a variety of parts would be difficult to stock and sell, especially if sold through the mail, since each bicycle seemingly would require individual fitting from a considerable selection of parts which would require to be stocked ready for sale and which would be hard for the customer to specify when remote from the source of parts.
Moreover, it was formerly thought necessary that the swivelling of the trailer, in order to conform to curves in the road, must take place around an approximately vertical axis, not around the bicycle seat post 72, which points backward from the vertical at an angle of 18 degrees more or less. This backward-pointing of the seat post would entail that the trailer, when pivoted to it, would be similarly tilted right to left when in a right-angular position as in FIG. 9--that is, tilted to a trailing angle of 18 degrees, like the angle of the seat post. With a 45-degree trailing angle as shown in FIG. 8, the tilt would be about 0.7 times 18 degrees or about 121/2 degrees. Such angles of tilt right to left would indeed be unacceptable if they occurred while one rides the bicycle at much more than a walking speed.